Method of making a spirallywound tube



0t- 18, 1966 H.T. BLAIR ETAL METHOD OF MAKING A SPIRALLY-WOUND TUBEFiled Nov. 27. 1963 l A @J United States Patent Office 3,279,333 METHODF MAKENG A SPIRALLY- WOUND TUBE Hugh T. Blair, Deerfield, and Richard L.Hatton, Elmhurst, Ill., assignors to Resinite Corporation, Chicago,

Ill., a corporation of Illinois Filed Nov. 27, 1963, Ser. No. 326,598Claims. (Cl. 93-94) This application is related to our copendingapplication Serial No. 121,882, led July 5, 1961, now abandoned.

This invention relates to tubular manufacture, and, more particularly,to a procedure for making a spirally- Wound rigid tube.

It is an object of this invention to provide a novel tube of thespirally-wound character and a method of producing the same--the tuberesulting from the practice of the invention being characterized bysuperior strength and versatility of application as compared with priorart tubes.

Another object is to provide a `method of constructing the tube whereinstrips or Webs of impregnated material are spirally wound in oppositedirections in adjacent layers and wherein unique pressure-providingmeans are utilized during the course of manufacture.

Still another object is .to provide a novel spirally-Wound tube and amethod of its manufacture wherein fibrous strips are cross yWound on amandrel and overlaid with an oriented iilm capable of shrinking whensubjected to heat, whereby an impregnant in the cross-Wound strips iscurable without the need for introducing the mandrel itself into thecuring station.

Other objects and advantages of the invention may be seen in the detailsof construction and operation set down in this specification.

The invention will be explained in conjunction with the accompanyingdrawing, in Which- FIG. 1 is an elevational view of apparatus employedin the fabrication of spirally-wound tubes;

FIG. 2 is a sectional view of the apparatus seen in FIG. 1 such as wouldbe viewed along the sight line 2-2 as applied to FIG. l;

FIG. 3 is a fragmentary elevational view, partially broken away, showingthe spirally-Wound tube just prior to curing;

FIG. 4 is an end elevational View of the tube of FIG. 3; and

FIG. 5 is a fragmentary sectional view of a completed tube.

In the illustration given, and with reference to FIG. 1, the numeraldesignates generally a spiral tube-winding machine. Provided as part ofthe machine is a housing 11 supported on a suitable pedestal 12. Thehousing 11 supports two or more spools of strip material (not shown),which are wrapped around a mandrel 13 (see FIG. 2). The spirally-woundweb strip material issuing from the housing 11 is designated kby thenumeral 14 in FIG. 1 and is seen to have convolutions extendingdownwardly from left to right as viewed in FIG. 1.

In one embodiment of the invention, as seen in FIGS. 3 and 4, theinnermost Winding may be of kraft paper, While the next adjacent winding(proceeding to the outside) is advantageously constructed of an orientedfilm material such as polyethylene terephthalate, marketed under thetrade name Mylar by E. I. du Pont de Nemours & C0., Wilmington,Delaware.

It is conventional practice to provide spirally-Wound tubes of thenature designated at 14, and these may be provided either on a rotatingmandrel, or a stationary mandrel (as contemplated here) in combinationwith a surface drive-a portion of the surface lbeing drive providedwithin the housing 11 and another portion being provided at 15 mountedon the pedestal 16. The dis- 3,279,333 Patented Uct. 18, 1966 charge endof the machine 10 usually includes a cut-off mechanism, schematicallyrepresented as at 17 for severing the spirally-wound tube in appropriatelengths.

Provided as part of the machine 10 is an opposite hand Winder generallydesignated 18 and a same hand Winder generally designated 19. Inspectionof FIG. 1 reveals that the opposite hand Winder provides aspirally-Wound strip 2t), the convolutions of which extend downrwardlyfrom right to left on the side in view, i.e., the opposite of theconvolutions designated 14.

In the embodiment of the invention presented herein,

the cross Winding or the winding immediately adjacent the I MylarWinding 14b is glass fiber designated 14e in FIG. 3. The fibrousunderlayer of kraft in the embodiment illustrated is designated 14a.

The same hand Winder Iprovides an overlapping layer by virtue of a webstrand 21, which again is glass fiber. This, it will be seen,corresponds in orientation 4to the convolutions initially provided anddesignated 14 in FIG. 1. Also provided from the Winder 19 is a secondWinding Which develops the layer designated 21a in FIG. 3 and in theembodiment illustrated is also of oriented polyethylene terepht'halate.Thus, what is provided is a spiral tube having one intermediate layerequipped with a righthand spiral land the next layer With a left-handspiral, with the outermost layer being an oriented polyester film.

The opposite hand Winder y18 .can be seen in FIG. 2 as well, andincludes a motor 23 mounted on par-t of the frame 24 provided as part ofthe surface drive 11S. Mounted for rota-tion Within the frame 24 is agear 25 suitably driven by .a motor 23 and which carries .a spool 26 ofweb material to be Wrapped about the tube produced by the machine -10 asat 14. It will be seen from the arrows 27 and 28 applied to FIG. 2 thatthe :direction of rotation -of the gear 25 is the same .as that of thetube 14 (variously the mandrel 13, if such is employed as therotationinducing element). However, the speed of rotation of .the ringgear 25 and its associated roll holder 26 is different, i.e., faster,than the rotation of the tube 14. As can be seen from FIG. 1, the spoolor roll holder 26 is supported on a shaft 29 inclined at an angle 0 tothe axis of the mandrel 13. It will be appare-nt that the angle 6 may-be changed for various Widths of tape and the speed of applicationthereof.

It is believed t-ha-t the invention Will be better under- .stood throughthe consideration of a spe-cie example, and for that pur-pose thefollowing is set down:

EXAMPLE Exemplary of the products capable fo being produced according.to the invention is a rigid coil form suitable for carrying electricalWiring and serving as an inductor coil, etc. Su-ch .a form may beconstructed of the glass fiber layers 21 and 21a when the same aresuitable impregnated with an epoxy .resin impregna-nt E. Such fibrousglass material already impregnated with an epoxy resin is commerciallyavailable as from Minnesota Mining & Manufacturing Company, of St. Paul,Minnesota, or the Houze Glass Co., of Point Marion, Pennsylvania.

To form a .tube of this nature ,and cure the same apart from t-hemandrel 13, We provide the first Winding 14a in the form of gummed kraftpaper. Depending upon the .amount of reinforcement needed initially,smaller or larger caliper ypaper may be employed. Over-lying thespirally wound kraft paper layer :14a is a layer of unoriented, heat-setpolyethylene terrephthalate. Such a iilm is initially heat-.set by being`subjected Ito elevated temperatures of from 15G-250 C. centigrade, andin this form is stable at temperatures u-p to the heat-settingtemperature. Specifically, Du pont Mylar 571 may be employed. As can beappreciated from FIG. 3, the layers 3 14a .and 14b are Wound .the samehand, .and with the convolutions in one layer overlapping .theconvolutions in the adjacent layer -to form a supporting core for theglass fiber tape Ilayers 14C -and 21.

Thereafter, at least one layer of Mylar of the oriented, non-heat-set`type is provided as a Wrapping. In this form, the film will shrink whensubjected :to .temperatures of the order of about 7080 C., and suchtempera-tures are employed during the curing of the epoxy resin withwhich the glass fiber strips 14o and 2.1 are impregnated.

Following rem-oval of the severed .tube from the mandrel 13, the tube iscured by residen-ce in an oven at about 150 C. for about one hour.During .this period, pressure is applied to the cross-Wound glass fiberlayers 14C and 21 by virtue of the shrinkage of Athe outer Mylar layer21a. It Will be appreciated that where increased pressure is indicated,additional layers of Mylar may be applied, :this product usually 4beingcommercially availa-ble :in `the order of one-half to three mils inthickness. The compressive .action provided by .the 4ou-ter Mylar layer21a forces the impregna-nt E through .the interface between thecross-Wound layers 14e .and 211 so as to develop a uniform, compact,fully integrated rigid tube.

Upon completion of the cure, the inner supponting layers 14a and 14h areremoved, as .is the outer compressive layer 21a. It Will be appreciatedthat other materials may be used in the inner supporting layers 14a and14!) which provide la release Winding relative to the epoxy adhesive.Other plastic materials such as cellulose acetate, polycarbonate, lorpolyethylene may be employed to provide this release activity.

I-n a specific instance of the practice of vthe invention, for a 1/2"diameter tube, We use for the kraft supporting winding .three layers of0.10 kraft having a Widtih of 1". For .the release winding 1411, weemploy one or two layers of 0.001 heat-set vMylar having a Width of 1%".to 11/2", which causes it to overlap .and insures against leakage of.the epoxy to the kraft.

By virtue of utilizing the compressive force of the outer Mylarwrapping, a rigid strong coil form can be developed from the windings14e and 21, even when the glass ber laye-rs have thicknesses as small asabout 0.020. Further, the glass fiber tape constructed core, when cured,has been found to possess a hoop stress of 175,000 p.s.i. and a flexuralmodulus of 9.6 106 p.s.i. yIt will be ap- :preciated that the strengthof the tube makes it advantageous in maintaining dimensional stabili-tywhich is essential in a lcoil form.

While in .the foregoing specification a detailed description of anembodiment of the invention has been set down for the purpose `ofexplanation thereof, many variations in .the details herein given may bemade by those skilled in -the art without departing from the spirit andscope of `the invention.

We claim:

1. In the manufacture of rigid tubes, the step of:

spirally winding first and second fibrous strips impregnated With athermosetting adhesive about a mandrel in crossed relation to form anelongated tube,

overwinding the said elongated `tube with oriented nonheat-setpolyethylene terephthalate lm to provide a cure assembly wherein vthesaid elongated tube is equipped with a film Wrapping,

removing the said .assembly from said mandrel and heating the saidassembly to 4a temperature sufficient tolthermally set said `adhesiveand shrink said film Wrapping about said elongated tube, and

removing said film wrapping from said elongated tube.

2. The method of claim 1 in which sai-d thermosettng adhesive is anepoxy resin.

3. The method of claim .1 in which said elongated `tube is provided withan inner supper-ting spirally-wound layer of kraft paper.

4. The method of claim 3 in which a layer of polyethylene terephfthalateis interposed between said kraft layer and said first and second fibrousstrips.

5. A method of manufacturing rigid tubes, comprising spirally Winding .acellulosic supporting strip on a mandrel, providing an overlying layerlof polyethylene `terephthalate on the irst-menteioned layer to provideeasy release -of a subsequent overlying layer therefrom, spirallywinding first and second fibrous strips impregnated with epoxy resin incrossed relation, ove-rwinding the said first and second strips with anon-heat-set polyethylene tereph- .thalate film to provide .a cureassembly, removing the cure assembly from said mandrel and heating the.assembly to a temperature suflicient to thermally set the epoxy resinand shrink the non-heat-se-t polyethylene terephthalate film about thecross-Wound first and second fibrous stri-ps, and, after curing,removing the brous supporting strip and polyethylene terephthalatewindings.

References Cited by the Examiner UNITED STATES PATENTS 2,723,705 11/1955Collins.

2,824,033 2/1958 Donaldson 156-190 XR 3,128,216 4/1964 Reed 156-190 XR3,185,759 5/ 1965 Sheehan.

BERNARD STICKNEY, Primm-y Examiner.

1. IN THE MANUFACTURE OF RIGID TUBES, THE STEP OF: SPIRALLY WINDINGFIRST AND SECOND FIBROUS STRIPS IMPREGNATED WITH A THERMOSETTINGADHESIVE ABOUT A MANDREL IN CROSSED RELATION TO FORM AN ELONGATED TUBE,OVERWINDING THE SAID ELONGATED TUBE WITH ORIENTED NONHEAT-SETPOLYETHYLENE TEREPHTHALATE FILM TO PROVIDE A CURE ASSEMBLY WHEREIN THESAID ELONGATED TUBE IS EQQUIPPED WITH A FILM WRAPPING, REMOVING THE SAIDASSEMBLY FROM SAID MANDREL AND HEATING THE SAID ASSEMBLY TO ATEMPERATURE SUFFICIENT